In general, a copying machine is used to copy an original without changing its size. This type of copying operation will be hereinafter referred to as "an equal magnification copying operation" when applicable. However, in the case where it is required to carry, arrange or store newspapers, large drawings or large documents for instance, it is desirable that the copying machine be capable of copying an original at a reduced size. This type of copying operation will be hereinafter referred to as "a reduction copying operation" when applicable. A variety of copying machines of this type are commercially available.
On the other hand, a copying machine having a mechanism for copying an original at an increased size (hereinafter referred to as "an enlargement copying operation" when applicable) can change the size of an original such as a small drawing into a larger one so that the original can be read with ease, or it can be used to make uniform the sizes of various documents such as changing size B5 literature or textbooks into size A4. However, it is unavoidable that such a copying machine employs an intricate mechanism and is bulky.
Accordingly, it is desirable to provide a compact copying machine which can carry out ordinary copying operations, namely, an equal magnification copying operation, an enlargement copying operation and a reduction copying operation, and can handle not only reduction factors such as a linear magnification of 0.866 for reducing an "A column" size document into a "B column" size document (for instance, from A3 to B4) and a linear magnification of 0.707 for reducing an "A column" size document into a different "A column" size (for instance from A3 to A4) and enlargement factors such as a linear magnification of 1.155 for increasing a "B column" size document into an "A column" size (for instance from B4 to A3) and a linear magnification of 1.414 for increasing an "A column" size document into another "A column" size (for instance from A5 to A4), but also a desired continuously variable magnification, for instance between 0.707 and 1.414 independent of the particular fixed "A column" and "B column" standard sizes.
The case will be considered where the image of an original is increased in size, for instance, by further increasing a movement set value in an application of an equal magnification or reduction copying system in which, as disclosed in Japanese Laid-Open Patent Application No. 65736/1978, the image forming lens and the mirror in the scanning optical system are moved. This system suffers from the difficulties that the required mechanism is intricate and it is necessary to manufacture the mechanism with high accuracy with the result that the manufacturing cost is considerably high. On the other hand, in a mechanism employing a zoom lens, in general, a long cam groove is formed in the lens frame and zooming is carried out by using the groove as a guide. This mechanism is disadvantageous in that the strength of the lens frame generally tends to be low and accordingly the lens frame is liable to be deformed, and that it is rather difficult to manufacture the lens frame. Furthermore, the mechanism is disadvantageous in that it is bulky as a whole. Especially in a copying machine, the zoom lens is usually driven by an electric motor. Therefore, in order to position the zoom lens at a predetermined distance, a stop mechanism and a motor control device must be used in combination with the result that the mechanism is necessarily intricate in construction and has a high manufacturing cost.